This invention generally relates to a mechanical pencil provided with a plurality of presharpened pieces of pencil lead stored within the pencil, more particularly an improvement in the writing implement of the type shown in U.S. Pat. No. 4,320,982.
The writing implement of U.S. Pat. No. 4,320,982, as shown in FIG. 1, is composed of an outer casing 10, a coil spring 30 disposed within outer casing 10, an inner tube 20 inserted through coil spring 30, inner tube 20 having a plurality of presharpened pieces of pencil lead 50 stored therewithin and having a lower end formed into a conical head 24 which has a pair of longitudinal slots 25, 26 to form into two semi-circular lead clamps 27.
Outer casing 10 is made of a hollow tube with the two opposite ends 13, 14 being respectively tapered to form a generally conical shape; a pair of depressions 11, 11 are provided near the lower end 13 to form two inner projections in casing 10 for stopping the lower end of coil spring 30. At a suitable position of the outer mid-part of inner tube 20 there is provided a pair of first protrusions 28 for receiving the upper end of coil spring 30, and near the outer upper end of inner tube 20 there is provided a pair of second protrusions 29 for engaging with the inner side of conical shaped upper end 14 of outer casing 10. Coil spring 30 thus biases inner tube 20 upwards relative to outer casing 10, causing lead clamps 27 at the lower end 13 of inner tube 20 to squeeze into the lower end of outer casing 10 to grip lead piece 51 in lead clamps 27.
Coil spring 30 has a lower end extending inwardly downwardly in a straight line at an appropriate angle with respect to the center axis of coil spring 30, to constitute a "lead-pushing member" 33, which is aligned with and moveably fitted into slot 25, so that tip 32 of lead-pushing member 33 abuts the rear end of lead piece 51. To replace lead piece 51 with the subsequent lead piece 52, inner tube 20 is first pushed down from the top relative to outer casing 10. The downward movement of inner tube 20 causes lead clamps 27 to extend from the lower end of outer casing 10 so as to relieve the pressure clamping lead piece 51, and at the same time lead pushing member 33 is pushed by the end wall 251 of slot 25 to swing outwardly so as to clear the way for the subsequent lead piece 52 to move down with inner tube 20. By releasing the downward pressure at the upper end of inner tube 20, inner tube 20 is then allowed to move upwardly by the spring force of coil spring 30, or to return to its original position. As inner tube 20 moves upwardly, lead-pushing member 33 is allowed to spring back inwardly in such a manner that tip 32 of lead-pushing member 33 comes in abutment with the rear end of second lead piece 52. During further upward movement of inner tube 20, lead-pushing member 33 blocks the upward movement of second lead piece 52, and as a result first lead piece 51 is pushed by second lead piece to drop out of lead clamps 27 while second lead piece 52 is pushed by lead-pushing member 33 into lead clamps 27.
In the above-described writing implement, an accurate alignment of lead-pushing member 33 with slot 25 is essential for a satistactory performance. However, because the last coil 31 at the lower end of coil spring 30 is received by a pair of projections formed by two depressions 11, 11, the lower end of coil spring 30, and consequently lead-pushing member 33, tends to tilt one way or the other, causing lead-pushing member 33 to come out of slot 25, or to misalign with slot 25 as shown in FIG. 2, or causing the tip 32 of the lead pushing member 33 to shift from the channel of inner tube 20 as shown in FIG. 3, to depart from the rear end of first pencil lead 51. As a result the lead-pushing member 33 will often not perform properly.
In view of the aforesaid problem with the writing implement of U.S. Pat. No. 4,320,982, this invention offers an improvement to such a writing implement by providing an annular supporting surface on the inner side of the lower end of the outer casing for seating the lower end of the coil spring 30 so as to prevent lead-pushing member 33 from tilting, or to avoid misalignment of the lead-pushing member 33 with respect to the slot of the clamps 27. The improvement further includes a longitudinal groove formed in the inner wall of the lower end of the outer casing to correspond to the slot of the clamps 27 so as to guide lead-pushing member 33.